Phase 2 Discovery is developing a synthetic melatonin analog (PD6735) for the treatment of sleep disorders. PD6735 is being developed as a safe and effective treatment for sleep disorders that lacks the side effects of current first-line sleep medications. Initial clinical studies indicate that PD6735 is safe and well tolerated in humans through the maximal dose tested, 20 mg. PD6735 produced a dose-response improvement in sleep latency in subjects with sleep onset insomnia (double-blind, placebo controlled, crossover study, N=1 9). The PD6735 effect on sleep latency was more pronounced at 20 mg than at 5 mg. The goal of the present Fast Track application is to determine whether the dose-response effect of PD6735 on sleep latency will be more pronounced at higher PD6735 doses. Phase 1 of this proposal will establish the safety and tolerability of PD6735 at 20 to 100 mg doses. Phase 2 will determine the effect of the 20 to 100 mg doses (or the maximum safe P 06735 dose identified in Phase I) on sleep latency in subjects with sleep-onset insomnia. The Specific Aims of the Phase 1 portion of this proposal are: Aim I: Evaluate the safety and tolerability of PD6735 at doses up to 100 mg. Oral doses of 20, 35, 50 and 100 mg will be employed. Aim 2: Determine the pharmacokinetics of PD6735 at doses up to 100 mg. Aim 3: Determine the pharmacodynamics of PD6735 at doses up to 100 mg. PD6735 effects on body temperature and subjective sleepiness will be evaluated. PROPOSED COMMERCIAL APPLICATIONS: Sleep disorders affect over 60 million Americans who spend more than $1.4 billion on sleep medications would have a competitive advantage over current first line therapies by virtue of possessing fewer side effects. As such, the melatonin analog should capture a substantial portion of this market.